Sorry for being late to the party here. First of all, you should get medical advice regarding diving from a physician who understands diving physiology and who has had the opportunity to thoroughly evaluate your personal history, speak with you, examine you, and review your test results. Take any other advice with a grain of salt -- and that includes mine as all I know is what you have mentioned in this thread.
I will speak in sweeping generalities. Whether or not to dive with underlying coronary artery disease is based on several factors -- exercise capacity, heart muscle function, evidence of a limitation of blood supply to your heart, and a personal risk/benefit decision by the diver. Again, IN GENERAL, if someone has a history of heart disease requiring stents or bypass surgery they can dive recreationally if they have good exercise tolerance (defined as reaching 13 METS on treadmill testing or the ability to sustain 6.5 METS for 20-25 minutes), have normal heart muscle function (left ventricular ejection fraction on echocardiography of > 50%), and no evidence of limitation to blood flow or significant exercise induced rhythm disturbances on exercise testing (I would not consider your two presumably PVCs on stress testing as significant). This having been said, divers with coronary artery disease are at an increased risk of heart attach and even death while scuba diving compared to the general population but this increase risk is quite small if the above criteria are met.
I would recommend you contact Divers Alert Network and ask for a referral to a diving physician in your area, preferably a cardiologist with knowledge of diving, and let that physician go over your individual case in detail. Scuba diving is a wonderful sport and, if you can do it safely, I would welcome you to our "club" with open arms. However, there is nothing down there worth dying for so see a diving physician and have a complete evaluation followed by a frank discussion.
Just my 2 cents.
Douglas Ebersole, MD
Interventional Cardiology, Watson Clinic LLP
Director, Structural Heart Program Lakeland Regional Health
Cardiology Consultant, Divers Alert Network
IANTD and TDI CCR Trimix Instructor
Now I can see why everyone was waiting for Dr. Ebersole's reply, as his answer is most helpful in making a good risk assessment!! I've managing risk fairly well most of my life, and I think that learning the art of managing risk is a life skill that should be taught throughout all formal and informal schooling. However, there's usually a dearth of reliable and useful information available from which to make much more than a guess, unless you want to devote more time than it is sometimes worth. Why so hard? Those without this skill are usually the ones offering up the advice, which often is either deficient, misleading, irrelevant, and obscures true gems like this one post. I have a few questions though to expand this answer just a bit, and then some background and opinions from me. But first, why his answer was significantly correct:
I found three articles that cover the METS requirements:
Achieving an Exercise Workload of =10 METS Predicts a Very Low Risk of Inducible Ischemia
This first full article covers just how important this is, in predicting the risks and also in improving your METS
Determining Heart Rates from MET Intensities
This covers a way to do the work so that you can use the heart rate to determine what your useful METS is in training.
Just from these articles and a few more, it is obvious to me that you should be able to KNOW that you can meet the guidelines he laid out. METS is extremely important, diving or not. I'd still like to know the effects of depth on cardiac health when virtually at rest, albeit at 90 feet.
Q - What are the reduction ratios various functionalities at different depths? Obviously, there's a huge difference in an experienced diver on a drift dive, trying to relax enough to end the dive with more air than the divemaster (>50 minutes w/reserve), vs. a new diver, scared close to panic, hunting for lobsters, actively fighting a current, or being actively chased. Yes, you want reserve capacity when you need it. But even at 50% o2 efficiency, an athlete is going to deplete most of his air in 15 minutes or less if swimming fast at depth. And since it take 4x the energy to go twice as fast, I'd get there half as fast, or use just twice the air. I guess I'm asking for the fitness aspect importance for CAD patients, and what aspects are at risk, if less fit.
Q - OTOH, how much less efficient are the cardiac arteries at 90ft? With a very low use of o2 at 90 ft, totally relaxed, ejection fraction shouldn't be much of a factor. ? But If stung badly, or a moray eel reaches for your hand or face, your going to panic for at least a few seconds, which adds a lot of stress and constriction, along with a good dose of adrenaline. Those that handle stress well, (and didn't get bitten), will likely be relatively unaffected. Those that don't relax though, are not going to have a good day and obviously would be stressing their hearts.
SCUBA vs snorkeling: I got into SCUBA after many years of snorkeling, mostly with NO partner. I'd do the stupid, worthless and dangerous hyperventilate to get my co2 higher, and o2 from 99% to 99.5%. Then I'd dive to 20-30 feet, and surface quickly when the urge to breath was too much. When in Cozumel once when I couldn't get to a good snorkeling site, they convinced me to do a shore dive. I quickly found that it was so much easier than the type of snorkeling I was doing, I'd never choose to free-dive again. In a few years, about 50 dives and certified open water, I'm now expert enough to think that know all I need to, and get myself into serious difficulty. Luckily I will likely always have a divemaster to try to limit that risk. Although I'm not stupid, my freediving by myself without understanding the co2 / o2 saturation factors, far exceed the risks I now take, SCUBA diving with heart disease.
In my case, although I've had two drug eluting stents, the two MI's I had, did minimal damage. I'm 71, my EF is still 55%-60, and slight occlusions haven't changed in over a decade. OTOH, I'm slightly out of shape right now, which could be remedied in a few months. So, I'd really like to know what effect that has, physiologically when diving. How much does being "out of shape", affect the risk for CAD patients? I think the METS articles I've included cover just how important this is--KNOW what your METS are, before you or I dive.
However, stuff happens! Currents get strong, wind and waves pick up, you can find yourself on the surface a long way from the boat or shore, etc. 13 METS is the equivalent of swimming against a one knot current for 20 minutes or so. That's how that value was chosen as it was felt that this was a reasonable level of fitness for recreational diving. Honestly, most scuba divers WITHOUT heart disease cannot reach 13 METS on treadmill testing (12 minutes on a standard Bruce protocol). That is why the idea of 6.5 METS for 20-25 minutes arose. From an exercise physiology standpoint, if you can hit 13 METS at peak exercise you should be able to sustain 1/2 of that (6.5 METS) for 20-25 minutes. With that in mind if you can walk 2 miles in 20 minutes you are probably fit enough for usual recreational diving.
